Kinetics of MgH2 formation by ball milling

Hydrogen (H2) absorption by metals, metal alloys, and more complex solids is a crucial issue on the road to the efficient H2 storage required by the hydrogen economy. The present study examines the reaction between Mg powder and gaseous H2 under ball milling conditions as a specific case study. Based on accurate kinetic evidence, we show that H2 absorption is governed by a combination of statistical and chemical contributions related, respectively, to the inherent nature of ball milling and the chemistry of the Mg–H2 system. The combination of the two factors determines the shape of the H2 absorption curve. Therefore, chemical information can be only obtained by disentangling the two contributions. To this aim, we propose a general method that can be extended to other chemical transformations activated by ball milling.